Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing slurries typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the slurry composition.
Conventional polishing compositions typically are not entirely satisfactory at planarizing copper layers found in semiconductor wafers. To meet industry demands, it is important to use a polishing composition that has a high polishing efficiency and removal rate and leaves a high quality polish with minimal surface defects. However, prior art polishing slurries for copper can have less than desirable polishing rates which are unable to satisfy throughput demands.
One approach to increase polishing rates for copper layers is to use more aggressive abrasives, such as aluminum oxide particles. There are several types of aluminum oxides, including α-alumina, γ-alumina, and θ-alumina. The use of γ-alumina and θ-alumina for polishing copper is well known in the art. See, for example, U.S. Pat. No. 6,521,574 and U.S. Pat. No. 6,436,811. However, α-alumina particles, the most aggressive type of aluminum oxide particles, are typically used to polish harder substrates that are less susceptible to scratching, such as noble metals. See U.S. Patent Application Publication 2002/0111027 A1.
Various strategies have been employed to obtain high removal rates by utilizing α-alumina while simultaneously minimizing scratching and erosion. For example, α-alumina particles can be coated with a surfactant to minimize scratches during polishing, as illustrated in U.S. Patent Application Publication 2003/0006396 A1. More commonly, a polishing slurry will contain a mixture of solids consisting of α-alumina particles and less abrasive solids. See, for example, U.S. Pat. No. 5,693,239, U.S. Pat. No. 6,444,139, U.S. Patent Application Publication 2004/0115944 A1, U.S. Patent Application Publication 2004/0157535 A1, and U.S. Patent Application Publication 2003/0181142 A1.
There remains a need for other compositions and methods for polishing copper-containing substrates. The invention provides such compositions and methods.